Process for regenerating spinning baths

ABSTRACT

BATHS USED FOR COAGULATING THREADS SPUN FROMA DIMNETHYLFORMAMIDE SOLUTION AND FOR STRETCHING THE SPUN THREADS ARE REGENERATED BY A PROCESS WHICH INCLUDES THE STEPS OF MIXING TOGETHER THE COAGULATING AND SPINNNING BATH, EXTRACTING THE MIXTRUE WITH DIMETHYLFROMAMIDE, RECYCLING THE RESIDUAL PARAFFINIC PHASE TO THE STRETCHING AND COAGULATING BATHS, TREATING THE EXTRACT PHASE WITH WATER TO SEPARATE IT INTO AN ORGANIC PHASE CONTAINING CUMENE WHICH IS RECYCLED TO THE COAGULATING BATH AND AN AQUEOUS PHSE FROM WHICH DIMETHYLFORMAMIDE IS SEPARATED BY DISTILLATION FREE FROM IMPURITIES.

United States Patent 3,641,233 PROCESS FOR REGENERATING SPINNING BATHS Cesare Reni and Luigi Lugo, Milan, Italy, assignors to Societa Italiana Resine S.p.A., Milan, Italy No Drawing. Filed Jan. 17, 1969, Ser. No. 792,155 Claims priority, application Italy, .Ian. 27, 1968, 12,064/68; Oct. 15, 1968, 827,220 Int. Cl. B2911 19/00 US. Cl. 264-179 7 Claims ABSTRACT OF THE DISCLOSURE Baths used for coagulating threads spun from a dimethylformamide solution and for stretching the spun threads are regenerated by a process which includes the steps of mixing together the coagulating and spinning baths, extracting the mixture With dimethylformamide, recycling the residual parafiinic phase to the stretching and coagulating baths, treating the extract phase with water to separate it into an organic phase containing cumene which is recycled to the coagulating bath and an aqueous phase from which dimethylformamide is separated by distillation free from impurities.

The invention relates to a process for regenerating spinning baths which are employed in manufacturing acrylic threads of 0.2 to 1.0 denier by spinning acrylonitrile copolymers.

More particularly, the invention relates to a wet spinning process wherein the acrylonitrile polymers, dissolved in dimethylformamide, are extruded in a coagulating bath comprising cumene and paraffins in addition to the solvent for the polymer, the threads being subsequently stretched in a stretching bath comprising essentially parafiins.

As We have described in a prior patent application, in manufacturing threads of low denier, acrylonitrile copolymers containing to 10% by weight of other monomers such as methacrylonitrile, vinyl acetate or, preferably, methyl and/or ethyl esters of the acrylic and/or methacrylic acids, of a molecular weight of 70,000 to 150,000 measured according to Staudinger, are dissolved in dimethylformamide so as to provide a copolymer concentration of 17 to 23% by weight.

The spinning solution is then extruded through dies having orifices of a diameter between 0.12 to 0.18 mm. into a coagulating bath containing cumene and 25 to 35 weight percent of dimethylformamide with a ratio by weight of dimet-hylformamide to cumene of 0.3/1 to 0.7/1, the remainder comprising linear paraffins having 10 to 16 carbon atoms in the molecule, in a quantity not exceeding in any case 25% by Weight.

To obtain satisfactory progress of the spinning process, the impurities in the coagulating bath must be maintained at a concentration below 0.05% by weight; moreover, the concentrations of the constituents of the bath are maintained as constant as' possible during coagulation.

In practice, the solution of the constituents of the desired concentration is continuously fed to the coagulating container, and a solution is continuously discharged, wherein the dimethylforrnamide concentration in the discharged solution does not exceed that in the feed solution by more than 3, or preferably, 2 percent by weight.

The solution discharged from the coagulating container is then regenerated to restore the concentration of the 3,641,233 Patented Feb. 8, 1972 coagulation bath constituents to the feed values and to remove impurities therefrom. As described in our prior patent application the stretching baths comprise linear parafiins having 10 to 16 carbon atoms in the molecule, in a quantity of at least 92% by weight. The dimethylformamide content of such baths should at any time be below 5%, preferably 3% by weight, the remainder being cumene.

In practice, in this case also, the paraflins are fed preferably in a substantially pure condition, a solution being discharged of which the paraffin content is not below 92% by weight. The solution discharged from the stretching bath should also be regenerated in order to remove impurities and restore the paraffin content to the desired values.

In manufacturing threads of a denier number of 0.2 to 1.0 it is essential for the impurities in the spinning bath to be maintained at very low values, more particularly below 0.05 by Weight, and it is further essential to maintain the concentrations of the bath constituents as constant as possible during the spinning process and within the above defined range.

It has now been found in accordance with the present invention that the coagulating and stretching baths can be regenerated by a single treatment which fully removes impurities and, on the other hand, simultaneously separates the constituents in a substantially pure condition.

According to the process of this invention, the solution discharged from the coagulating bath is mixed with the solution discharged from the stretching bath; the resulting mixture is subjected to liquid/liquid extraction by utilizing as a solvent dimethylformamide, so as to obtain a refined product substantially comprising the previously described paraffins and an extract substantially comprising dimethylformamide and cumene. The extracted phase is admixed with water in order to separate a substantially pure cumene phase and an aqueous solution of dimethylformamide, which contains the impurities and from which water first and dimethylformamide next is distilled.

The constituents separated as above can be directly employed in the spinning process, excess dimethylformamide being utilized at the extraction stage.

Thus, by the process of the invention the solution which is discharged from the coagulating bath comprising cumene, dimethylformamide and, possibly, p araffins, and enriched with impurities and dimethylformamide With respect to the feed solution, is mixed with the solution discharged from the stretching bath.

The latter mainly comprises parafiins and is rich in impurities, as Well as cumene and dimethylformamide with respect to the feed.

The solutions discharged from the coagulation and stretching steps are of a composition within the limits defined above.

The resulting mixture is fed to a position intermediate the top and foot of an extraction column having 5 to 10 theoretical trays.

At the first or second tray at the top of the column there is fed in a solvent, which comprises dimethylformamide containing, in the preferred embodiment, 0.5 to 10% by weight of water. The ratio of the solvent to the mixture discharged from the spinning baths is maintained during the extraction within a range of 2/1 to 12/1.

During extraction the temperature is preferably maintained at or slightly above room temperature.

In the preferred embodiment, to the extraction column is fed, in addition to the mixture discharged from the coagulation and stretching baths, paratfins and cumene which separate by stratification as the lighter phase in the thread wash baths. This results at the top of the extraction column in a refined phase comprising parafiins with small quantities of dimethylformamide and cumene.

A fraction of the refined phase is recycled as such to the coagulating bath, the remainder being employed as feed to the stretching bath preferably after treatment with small quantities of water (usually less than 15% by weight with respect to paratfins) in order to remove dimethylformamide.

The resulting aqueous solution of dimethylformamide c?n be usefully employed in the manner described herea ter.

An extracted phase is obtained at the foot of the extraction column, which comprises dimethylformamide, cumene and impurities.

The extracted phase is treated with water in a quantity of 0.5 to parts, preferably 1 to 3 parts by weight to one part b weight dimethylformamide.

In a preferred embodiment, the water from the thread wash baths is utilised, which has dissolved therein small quantitles of dimethylformamide, and the diluted aqueous dimethylformamide obtained from the wash of the refined phase. This yields an organic phase which essentially comprises cumene and is recycled to the coagulating bath, and an aqueous phase of the dimethylformamide containing the impurities. The aqueous phase is subjected to distillation in order to first separate water therefrom and, secondly, dimethylformamide, the latter separation being carried out in the preferred embodiment by the thin layer evaporating technique, more particularly with a Luwaevaporator equipped with scraper blades.

Dimethylformamide is recycled in part to the coagulating bath and to the extraction column, respectively, and is utilized in part in forming the spinning solution.

The process of the invention is advantageous in that it provides a substantial total recovery of the spinning bath constituents, so that but slight replenishments are required. The dimethylformamide losses are in practice always below about 0.05 kg. to one kg. of manufactured thread, the cumene and paraffin losses being negligible.

Moreover, the spinning baths are of a very low impurity content, so that threads can be continuously manufactured from acrylonitrile polymers, which are of low denier number, such as 0.2 to 1.0.

Finally, the process of the invention, which can be rendered continuous by simple arrangements, atfords regeneration by a single treatment of the spinning and stretching baths, which strongly ditfer in composition.

Example An acrylonitrile copolymer containing by weight methylmethacrylate, of a molecular weight of 80,000, measured according to Staudinger, was dissolved in dimethylformamide to yield a spinning solution containing 18% by weight of copolymer. This solution was filtered, evacuated and extruded into a coagulating bath at a linear inlet rate of approximately 2.7 m./min. through a die whose orifices are 0.12 mm. in diameter. The feed rate of the spinning solution was 2.4 kg./hr., and the coagulating bath was maintained at a temperature of 60 C.

To the bottom of the coagulating bath there was fed continuously, at a rate of about 90 kg./hr., a solution comprising 60% by weight cumene, 30% dimethylformamide and 10% paratfins. The cumene was of commercial grade with a concentration exceeding 99.5% by Weight; the paraflins were a mixture of linear chain products containing 10 to 13 carbon atoms in the molecule, with an average number of 11.6 carbon atoms in the molecule.

A solution was continuously discharged from the coagulating bath, consisting of 58.7% by weight cumene, 31.5% dimethylformamide and 9.8% paraffins.

The threads, which were travelling in the same direction as the coagulating solution, were collected at the top of the bath at a rate of 10 m./min., and were then stretched ten times in a stretching bath at a temperature of 115 C.

The stretching bath was fed with about 8.7 kg/hr. of the previously described paraflins, a paraffin solution being discharged containing approximately 3% cumene and 1.5% dimethylformamide. The threads were finally washed in water baths and dried. The result is a thread of 0.5 denier and a resiliency of 3.3 g./ denier.

The solutions discharged from the coagulating and stretching baths were mixed together and fed at a rate of about kg./hr. to a region intermediate the top and foot of an extraction column having 8 theoretical trays; simultaneously the organic products were fed which mainly comprised small quantities of cumene, and these separated as the lighter phase in the water thread wash baths.

At the second theoretical tray of the extraction column, at the end at which the refined product was separated, dimethylformamide was supplied in a quantity of about 630 kg./hr. together with about 42 kg./hr. of the aqueous solutions from the thread wash baths and refined product wash, which contained small quantities of dimethylformamide.

The extraction was carried out at a temperature of about 30 C., about 18 kg./hr. of refined product being collected at the column top and essentially comprising paraffins containing small quantities of cumene and dimethylformamide.

About 50% of the refined product was recycled as such to the coagulating bath, dimethylformamide being removed from the remaining fraction by treatment with approximately 1 kg./hr. of the aqueous solutions from the thread wash baths and subsequent decantation. This yielded an aqueous layer containing dimethylformamide, which was conveyed to the extraction column, as described above, and an organic layer which was directly fed to the stretching bath.

The extract was recovered at the foot of the extraction column and was treated with about 600 kg./hr. water and conveyed to a decanting apparatus. An organic phase was obtained essentially comprising cumene, which was recycled to the coagulating bath, as well as an aqueous layer containing the dimethylformamide and impurities, from which water first, and dimethylformamide next was distilled in vacuum in a Luwa-evaporator equipped with scraper blades.

The resulting dimethylformamide was utilized partly as a recycle to the extraction column, and partly as a recycle to the spinning bath, the remaining fraction being employed for producing the spinning solution.

WVhat is claimed is:

1. A process for regenerating spinning baths used in the conversion of acrylonitrile copolymers to threads having a denier of from 0.2 to 1.0 wherein a spinning solution of said copolymer in dimethylformamide is extruded into a coagulating bath comprising, by weight, from 25 to 35% dimethylformamide, cumene wherein the dimethylformamide/cumene weight ratio varies from 0.3/1 to 0.7/1, the remainder being linear paraffins having from 10 to 16 carbon atoms, and wherein the resulting threads are stretched in a stretching bath consisting essentially of said paraffins, said process comprising:

(a) mixing a first solution discharged from said coagulating bath, said first solution being enriched in dimethylformamide and impurities with respect to the initial coagulating bath with a second solution discharged from said stretching bath, said second solution being enriched in cumene, dimethylformamide and impurities, with respect to said initial stretching bath, to thereby form a mixture;

(b) subjecting all of said mixture to liquid/liquid countercurrent extraction with dimethylformamide containing from 0.5 to 10% water by weight in a weight ratio of said dimethylformamide to said mixture of from 2:1 to- 12:1 to thereby produce a refined phase consisting essentially of said paraifins and an extracted phase consisting essentially of cumene and dimethylformamide;

() recycling a first portion of said refined phase to said stretching bath after removing dimethylf ormamide from said first portion by adding water to said first portion and removing said dimethylformamide as an aqueous solution thereof;

(d) recycling the remaining portion of said refined phase to said coagulating bath;

(e) adding from 0.5 to parts, by weight, based on the weight of said dimethylformamide in said extracted phase, of water to said extracted phase to produce an organic phase consisting essentially of cumene and an aqueous phase containing dimethylformamide;

(f) recycling said organic phase to said coagulating bath;

(g) separating Water and then dimethylformamide from said aqueous phase by distillation;

(h) recycling a portion of said dimethylformamide to said coagulating bath; and

(i) utilizing the remaining dimethylformamide to prepare said spinning solution.

2. The process as claimed in claim 1 wherein the increase in concentration of dimethylformamide in the coagulating bath, between the feed solution and discharged solution, is below 3 percent by weight.

3. The process as claimed in claim 1, wherein the solution discharged from the coagulating bath mixed with the solution discharged from the stretching bath is fed to a region intermediate the top and foot of an extraction column, an extraction solvent of dimethylformamide or dimethylformamide containing 0.5 to weight percent water being fed to the column at the end at which the refined phase is separated, so as to obtain an extracted phase consisting essentially of cumene and dimethylformamide and a refined phase consisting essentially of said parafi'ins.

4. The process as claimed in claim 1, wherein dimethylformamide is removed from said first portion of said refined phase by treatment with water in a quantity not exceeding 15% by weight with respect to the weight of said parafiins in said first portion.

5. The process as in claim 2, wherein the increase in concentration is below 2% by weight.

6. The process as in claim 1 wherein said extraction is conducted at a temperature of about room temperature.

7. The process as in claim 1 wherein said extracted phase is treated with from 1 to 3 parts, by weight, based on the weight of said dimethylformamide in said extracted phase of water.

References Cited UNITED STATES PATENTS 2,957,748 10/ 1960 Liesberg 264-206 2,967,085 1/1961 Sanden et al. 264182 2,967,086 1/1961 Sanden et a1. 264-182 3,449,485 6/1969 Costa et a1. 264--182 FOREIGN PATENTS 706,154 3/1954 Great Britain 264-182 708,078 4/1954 Great Britain 264-182 541,104 5/1957 Canada 264-182 587,577 11/1959 Canada 264-182 JAY H. WOO, Primary Examiner US. Cl. X.R. 26437, 182 

